The present invention relates to a cement additive capable of effectively reducing the air entraining property and producing an outstanding flowability retaining effect.
Since 1981 when early degradation of concrete structures posed a social problem, it has been strongly demanded that the amount of water per unit volume of concrete be reduced so that the workability and durability of concrete may be improved. In such circumstances, technological innovations have been made in relation to the cement admixture which exerts a great influences on the quality and performance characteristics of cement mixes.
In particular, with regard to polycarboxylic acid type cement dispersing agents, which show higher water-reducing effects as compared with the conventional cement dispersing agents, such as those of the naphthalene type, a number of proposals have been made for using them as high-performance air-entraining and water-reducing agents. However, such polycarboxylic acid type cement additives exhibit potent air entraining properties and, furthermore, the amount of air entrained by them varies with time and it is difficult to control the variation, so that desired concrete strength can hardly be attained. Therefore, admixture manufacturers have made energetic investigations to develop high-performance air-entraining and water-reducing agents with a decreased air entraining property.
In JP Kokai H06-298557, there are proposed polymers obtained by polymerizing a polyethylene glycol monoester monomer (A), a polypropylene glycol monoester monomer (B) and an unsaturated carboxylic acid monomer (C) and, in JP Kokai H06-279082, there are proposed polymers obtained by polymerizing a monomer (A) derived from (meth)acrylic acid by blockwise addition of (poly)propylene oxide-polyethylene oxide-(poly)propylene oxide and an unsaturated carboxylic acid monomer (C). Further, in JP Kokai H06-321596, there are proposed copolymers obtained by copolymerizing a polyethylene polypropylene glycol monoester monomer (A) or polypropylene polyethylene glycol monoester monomer (B) and an unsaturated carboxylic acid monomer (C).
Under the present circumstances, however, the polymers with polypropylene glycol chains and polyethylene glycol chains introduced therein separately as disclosed in JP Kokai H06-298557 as well as the polymers with polypropylene glycol-polyethylene glycol chains alone introduced therein as disclosed in JP Kokai H06-279082, JP Kokai H06-298557 or JP Kokai H06-321596 are still incompetent for effectively reducing air entraining property and providing good flowability.
In view of the prior art mentioned above, the present invention has for its object to provide a cement additive which has a reduced air entraining property and can provide good flowability.
The present invention is thus directed to a cement additive which comprises a copolymer (A) obtainable by polymerizing a monomer mixture (K), wherein;
said monomer mixture (K) comprises a polyalkylene glycol ester monomer (I) represented by the general formula (1): 
xe2x80x83[wherein R1 represents a hydrogen atom or a methyl group, the R2O groups are the same or different and each represents an oxyalkylene group containing 2 to 18 carbon atoms and the majority thereof are oxyalkylene groups containing not less than 3 carbon atoms, R3 represents an aliphatic hydrocarbon group containing 4 to 30 carbon atoms or an alicyclic hydrocarbon group containing 4 to 30 carbon atoms, and n represents the average number of moles of oxyalkylene groups added and is a number of 5 to 300, with the condition that the average number of moles of oxyalkylene groups containing not less than 3 carbon atoms as added is not less than 5];
a polyalkylene glycol ester monomer (II) represented by the general formula (2): 
xe2x80x83[wherein R4 represents a hydrogen atom or a methyl group, the R5O groups are the same or different and each represents an oxyalkylene group containing 2 to 18 carbon atoms and the majority thereof are oxyethylene groups, R6 represents a hydrocarbon group containing 1 to 30 carbon atoms, and m represents the average number of moles of oxyalkylene groups added and is a number of 2 to 300]; and
a carboxylic acid monomer (III) represented by the general formula (3): 
xe2x80x83[wherein R7 represents a hydrogen atom or a methyl group, and M represents a hydrogen atom, a metal atom, an ammonium group or an organic amine group].
The present invention is also directed to a method of producing said copolymer (A) for use as a cement additive,
which comprises polymerizing a monomer mixture (K),
the polymerization reaction being effected by adding a polymerization initiator to a solution containing a monomer mixture (K), and
said monomer mixture (K) comprising said polyalkylene glycol ester monomer (I) of general formula (1), said polyalkylene glycol ester monomer (II) of general formula (2) and said carboxylic acid monomer (III) of general formula (3).
The present invention is further directed to a cement additive comprising the polymer (B),
wherein a 0.1% by weight aqueous solution the polymer (B) treated with ether has a surface tension of 0.1 to 50 mN/m and an ultraviolet transmittance at 600 nm of 30 to 100%.
The present invention is still further directed to a cement admixture which comprises an air-entraining agent and said cement additive.